Dual-Modified Cellulose Nanofiber Membranes with Boosted Surface Charge for High-Performance Osmotic Energy...

Area of Science:

• Materials Science
• Nanotechnology
• Renewable Energy

Background:

• Nanofluidics holds promise for osmotic energy conversion, but low nanomaterial surface charge limits membrane ion selectivity, permeability, and power output.
• Current single-step modification methods face substitution limits, hindering substantial surface charge achievement in membranes.
• Optimizing nanochannel structure alongside surface charge is crucial for efficient ion transport.

Purpose of the Study:

• To develop novel, oppositely charged cellulose nanofiber membranes with enhanced ion selectivity and permeability for osmotic energy conversion.
• To overcome the limitations of single-step modifications using a dual-modification strategy.
• To investigate the synergistic effects of enhanced surface charge and tailored nanochannels on membrane performance.

Main Methods:

• A dual-modification strategy involving small-molecule functionalization and polymer grafting was employed to create highly charged cellulose nanofiber membranes.
• Systematic investigation of the membranes' surface charge, nanochannel structure, and ion transport properties.
• Fabrication and testing of a reverse electrodialysis (RED) unit utilizing the developed membranes to assess power density and scalability.

Main Results:

• The dual-modified membranes exhibited significantly enhanced surface charge and optimized nanochannel structures, leading to improved ion selectivity (t_+ of 0.97).
• Negatively and positively charged membranes achieved power densities of 5.1 W·m⁻² and 4.6 W·m⁻², respectively, representing substantial improvements over pristine membranes.
• A RED unit with these membranes delivered a power density of 12.9 W·m⁻² (5/0.01 M) and generated 2.5 V with 15 membrane pairs, demonstrating practical scalability.

Conclusions:

• The proposed dual-modification strategy effectively enhances surface charge and maintains optimal nanochannel structure in cellulose nanofiber membranes.
• These engineered membranes exhibit superior ion selectivity and transport, leading to significantly boosted power output for osmotic energy conversion.
• The developed membranes offer a sustainable, low-cost, and scalable solution for efficient osmotic energy harvesting, advancing nanofluidic applications.